1. Field of the Invention
The present invention relates to a magnetic recording medium and to a method of manufacturing the same. More particularly, the present invention relates to a high recording capacity magnetic recording medium affording both good electromagnetic characteristics and running stability, and to a method of manufacturing the same.
2. Discussion of the Background
Magnetic recording media in the form of particulate magnetic recording media having a magnetic layer fabricated by coating a magnetic coating material, comprising ferromagnetic powder and a binder dispersed in a solvent, on a nonmagnetic support, and metal thin-film type magnetic recording media, having ferromagnetic powder deposited in the form of a film on a nonmagnetic support, are known. Particulate magnetic recording media are known to be superior from the perspectives of productivity and general-purpose properties.
Various nonmagnetic particles are employed in particulate magnetic recording media as an abrasive in the nonmagnetic layer (see Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-45056, Japanese Unexamined Patent Publication (KOKAI) No. 2000-12315, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 1-87672, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 1-88914, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-170713, and Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-319516, which are expressly incorporated herein by reference in their entirety.
In recent years, as the information being recorded has grown more diverse and increased in capacity, data backup tape products with high recording capacities have been brought to market. To achieve higher recording capacities, the magnetic layer has become increasingly thin. By contrast, in magnetic recording media sequentially comprised of a nonmagnetic support, a nonmagnetic layer, and a magnetic layer, the nonmagnetic layer has normally been formed of a comparatively thick film relative to the magnetic layer for ensuring calendaring moldability and the like. However, there are limits to the increase in capacity that can be achieved by reducing the thickness of the magnetic layer alone. Thus, when the present inventors attempted to reduce the thickness of the nonmagnetic layer in the design of a conventional magnetic recording medium, they encountered the phenomena of compromised electromagnetic characteristics and reduced running stability, making it difficult to obtain a magnetic recording medium of high reliability that permitted both recording and reproduction. One reason for this was that the status of protrusions from the surface of the magnetic layer in the form of abrasive contained in the magnetic layer differed from that of conventional magnetic recording media having thick nonmagnetic layers.